In air-conditioning and refrigerative units, fluorine hydrocarbons and very often ammonia are employed as the coolants, the boiling-points of which may lie considerably below 0.degree. C., depending on whatever their chemical composition happens to be, and ambient pressure. Thus, for example, the boiling point of CF.sub.2 Cl.sub.2 is -29.8.degree. C., and that of CF.sub.3 Cl, -81.5.degree. C. During maintenance and repair operations, refrigerants need to be decanted from their units. For this purpose, refrigerants under pressure are gathered in steel cylinders. After closing the cylinder valve, a residual amount of the refrigerant will remain behind in the unit which cannot be collected and thus is released into the atmosphere. This means of course that a part of the refrigerant is lost, and, in addition, certain coolants are of a nature which makes them a hazard to the environment.